<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>累加</title>
    <style>
        #b{
            width: 400px;
            height: 400px;
        }
        .a{
            width: 100px;
            height: 100px;
            border: 1px solid #000;
        }
    </style>
</head>
<body>
    <div id="b">
        <div class="a">1</div>
        <div class="a">1</div>
        <div class="a">1</div>
        <div class="a">1</div>
    </div>
</body>
<script>
     var sum = 0
     for(var i=1; i<=100; i++){
         if(i % 2 == 0)
         sum +=i;
     }
     console.log(sum)
</script>
</html>